Battery

ABSTRACT

A negative lower gasket has a rib disposed along the outer periphery of a flat portion having a base of a negative current collector disposed thereat. The height of the rib is set to be more than a thickness of the negative lower gasket. The rib may be disposed only at a portion corresponding to a position where legs project from the base of the negative current collector at the outer periphery of the flat portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a battery including a nonaqueouselectrolytic secondary battery.

2. Description of the Related Art

A battery such as a nonaqueous electrolytic secondary battery includes apositive current collector and a negative current collector forelectrically connecting a positive electrode and a negative electrode inan electrode assembly contained inside of a battery case to a positiveexternal terminal and a negative external terminal, respectively. A baseof the current collector is fixed to a cover for sealing an upperopening of the battery case by means such as caulking using, forexample, a rivet. A gasket is interposed between the base of the currentcollector and a lower surface of the cover. (See Japanese UnexaminedPatent Application Publication No. 2009-277603 (FIG. 2).)

A current collector on a negative electrode side of, for example, alithium ion battery need be securely insulated from a battery case and acover (i.e., a package) via a gasket. However, a satisfactoryconsideration is not always made on insulation between a currentcollector and a package via a gasket in conventional batteries inclusiveof the battery disclosed in Japanese Unexamined Patent ApplicationPublication No. 2009-277603.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a gasket capable ofsecurely insulating a current collector from a package.

A battery according to the present invention includes: a currentcollector having a base which is disposed at an inner surface of apackage and is electrically connected to an external terminal and aconnector which projects from the base and is electrically connected toan electrode assembly contained inside of the package; and a gaskethaving a body interposed between the base of the current collector andthe package and a rib which is disposed at least at a portioncorresponding to a position at the outer peripheral edge of the bodywhere the connector projects from the base of the current collector andhas a height more than a thickness of the base of the current collector.

The gasket is provided with the rib disposed along the outer peripheraledge of the body interposed between the base of the current collectorand the package. The rib has the height greater than the thickness ofthe base of the current collector. This rib satisfactorily ensures aninsulation distance between the current collector and the package, thussecurely insulating the current collector from the package.

The gasket preferably includes a contained portion which is contained ina recess formed at the inner surface of the package.

The contained portion of the gasket interposed between the currentcollector and the package is contained in the recess formed at the innersurface of the package. Consequently, the projection of the gasket fromthe inner surface of the package can be suppressed to the minimum. Thesuppression of the projection of the gasket enables the end of theelectrode assembly to be disposed sufficiently in the proximity of theinner surface of the package. Thus, energy density can be enhanced byincreasing the occupancy of the electrode assembly with respect to thevolume of the battery case.

Moreover, the wall surface defining the recess of the package is formedinto not a flat shape but a recessed shape. The recessed wall surfacerestricts or restrains the position of the contained portion of thegasket which is contained in the recess. In other words, the recess ofthe package and the contained portion of the gasket are not brought intocontact with each other on the plane. Consequently, the gasket can beprevented from being rotated with respect to the package. Therefore, aload can be prevented from exerting on a part of the gasket (e.g., acaulked and joined portion via a rivet) which may be caused by suchrotation of the gasket.

The current collector preferably includes a base which is electricallyconnected to the external terminal and a connector which projects fromthe base and is electrically connected to the electrode assembly; andthe contained portion of the gasket should preferably include a caulkedportion which is caulked and joined to the package together with thebase, the thickness of the caulked portion being greater than those ofother portions of the gasket.

With the configuration, the weight of the gasket and a material requiredfor fabricating the gasket can be reduced while enhancing air-tightnessof the gasket.

A clearance is preferably defined between the surroundings of thecontained portion of the gasket and the wall surface of the recess ofthe package.

With the configuration, a clearance for deformation (relief) in a planardirection with respect to compression in a thickness direction of acaulked portion can be secured at the time of caulking and joining, sothat a damage such as a crack of the gasket can be securely prevented atthe time of caulking and joining.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a battery in an preferredembodiment according to the present invention;

FIG. 2 is a perspective view of a cover;

FIG. 3 is an enlarged view of a section III of FIG. 1;

FIG. 4 is an enlarged view of a section IV of FIG. 1;

FIG. 5 is a perspective view of the surroundings of a lower gasket onthe side of a lower surface of the cover;

FIG. 6 is a partly cross-sectional perspective view of the surroundingsof the lower gasket on the side of the lower surface of the cover;

FIG. 7 is a cross-sectional view taken along a line VII-VII of FIG. 2;

FIG. 8 is a cross-sectional view taken along a line VIII-VIII of FIG. 2;

FIG. 9 is an exploded perspective view of the lower gasket and anegative current collector, as viewed from the bottom; and

FIG. 10 is an exploded perspective view of the lower gasket and thenegative current collector, as viewed from the top.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A detailed description will be given below of an embodiment according tothe present invention with reference to the attached drawings.

FIG. 1 shows a nonaqueous electrolytic secondary battery 1 (hereinaftersimply referred to as a battery) in an embodiment according to thepresent invention. An electrode assembly 3 of the battery 1 is housed ina battery case 2 which is made of aluminum or an aluminum alloy and isformed into a rectangular parallelepiped shape. An upper opening of thebattery case 2 is sealed by a cover 4. The battery case 2 and the cover4 constitute a package. The upper surfaces of a negative externalterminal 14 and a positive external terminal 15 are exposed to theoutside of the cover 4.

The electrode assembly 3 includes a negative electrode formed of acopper foil, a positive electrode formed of an aluminum foil, and aseparator 7 made of a porous resin film and interposed in a wound mannerbetween the negative electrode and the positive electrode. In theelectrode assembly 3, the negative electrode is electrically connectedto the negative external terminal 14 via a negative current collector 12whereas the positive electrode is electrically connected to the positiveexternal terminal 15 via a positive current collector 13.

As shown in FIG. 2, the cover 4 is made of an elongated metallic plateformed into a rectangular shape, as viewed on plane. The cover 4includes a safe valve 8 near the center thereof in a longitudinaldirection and a liquid injection hole 9 formed at one end thereof.

An engagement receiving portion 11 formed into a substantiallyrectangular shape, as viewed on plane, is formed at both ends of thecover 4 so as to expand upward from an upper surface 4 b. The engagementreceiving portion 11 has an engagement recess 11 a formed by depressinga lower surface 4 a of the cover 4. Moreover, a through hole 11 b isformed at the center of a ceiling constituting the engagement recess 11a.

As shown in FIGS. 3 and 5 to 8, the negative external terminal 14 andthe negative current collector 12 are fitted to the engagement receivingportion 11 on the left via an upper gasket 16 and a negative lowergasket 17 which are made of an insulating resin, respectively.

Referring to FIGS. 2 to 4, 6, and 7, explanation will be made on theupper gasket 16. The upper gasket 16 is a resin part having a terminalholding recess 16 b on the upper side and a mounting recess 16 c on thelower side which are partitioned by a partition wall 16 a. A cylindricalportion 16 d extending downward and having openings at both ends thereofis formed at the center of the partition wall 16 a. The upper gasket 16is put on the engagement receiving portion 11 from above, and then,attached to the cover 4 by containing the engagement receiving portion11 in the mounting recess 16 c. The cylindrical portion 16 d is insertedinto the through hole 11 b to intrude into the engagement recess 11 a.Moreover, engagement projections 19 projecting from the upper surface 4b of the cover 4 are inserted into engagement holes 16 f formed at twotongue pieces 16 e provided in the upper gasket 16.

Referring to FIGS. 3 and 5 to 10, explanation will be made on thenegative lower gasket 17. The negative lower gasket 17 includes anexpanded portion 17 a which is to be contained inside of the engagementrecess 11 a of the cover 4, and a flat portion 17 b which is disposed ina region adjacent to the engagement recess 11 a at the lower surface 4 aof the cover 4 and is formed into a substantially rectangular shape.

As most clearly shown in FIGS. 9 and 10, the expanded portion 17 a ofthe negative lower gasket 17 includes a caulked portion 17 c which isdisposed with a step in a height direction with respect to the flatportion 17 b and extends in parallel to the flat portion 17 b.

The caulked portion 17 c in the negative lower gasket 17 is disposed onone short side of the flat portion 17 b, and further, is connected viathree vertical walls 17 d, 17 e, and 17 f to the flat portion 17 b. Athrough hole 17 g penetrating in a thickness direction is formed in thecaulked portion 17 c. As shown in FIGS. 3 and 6, the cylindrical portion16 d of the upper gasket 16 is inserted into the through hole 17 garound the lower end thereof.

As most clearly shown in FIG. 9, a rib 17 h projecting downward isdisposed at the outer peripheral edge of the flat portion 17 b of thenegative lower gasket 17 except a part of one short side (a short sideforward in FIG. 9).

Referring to FIGS. 3 and 5 to 7, a description will be given of thenegative external terminal 14. The negative external terminal 14includes an aluminum plate-like member 21 having a rectangular shape, asviewed on plane, and a copper rivet 22. A flange 22 a is press-fittedinto a through hole 21 a formed at the center of the plate-like member21 so that the rivet 22 is fixed to the plate-like member 21 in thestate in which a shaft 22 b projects. The plate-like member 21 iscontained in the terminal holding recess 16 b of the upper gasket 16.

Referring to FIGS. 3 and 5 to 10, explanation will be made on thenegative current collector 12. The copper negative current collector 12includes a base 12 a and a pair of legs (connectors) 12 b and 12 b. Thebase 12 a includes a fixed portion 12 c, which is contained inside ofthe engagement recess 11 a formed at the lower surface 4 a of the cover4 and is fitted to the lower side of the caulked portion 17 c in theexpanded portion 17 a of the negative lower gasket 17, and a mount 12 dto be fitted onto the lower side of the flat portion 17 b of thenegative lower gasket 17 at a position adjacent to the engagement recess11 a. A through hole 12 e penetrating in a thickness direction is formedin the fixed portion 12 c. The fixed portion 12 c and the mount 12 d,which are stepwise different in the height direction, are connected viaa vertical wall 12 f. The legs 12 b and 12 b extend downward from themount 12 d. The legs 12 b and 12 b are electrically connected to andmechanically coupled to the negative electrode in the electrode assembly3 via a clip 10 schematically shown only in FIG. 1.

The shaft 22 b of the rivet 22 in the negative external terminal 14 isinserted into the cylindrical portion 16 d of the upper gasket 16, thethrough hole 17 g formed in the caulked portion 17 c of the negativelower gasket 17, and the through hole 12 e formed in the fixed portion12 c of the negative current collector 12, and then, the tip is widenedunder pressure, thereby forming a large-diameter portion 22 c.Consequently, the negative external terminal 14, the upper casket 16,the caulked portion 17 c of the negative lower gasket 17, and the base12 a of the negative current collector 12 are securely caulked andjoined to the cover 4. Moreover, owing to the caulking and joining, thenegative current collector 12 is electrically connected to the negativeexternal terminal 14.

Referring to FIGS. 1 to 3, the positive external terminal 15 and thepositive current collector 13 are fixed to the engagement receivingportion 11 on the right side via the upper gasket 16 and a positivelower gasket 18 which are made of an insulating resin, respectively.

In the same manner as the side of the negative electrode, the uppergasket 16 is attached to the engagement receiving portion 11. Moreover,the positive lower gasket 18 is formed into a plate having a throughhole 18 a, and is disposed inside of the engagement recess 11 a.

The aluminum positive external terminal 15 includes a plate-like member15 a formed into a rectangular shape, as viewed on plane, and acylindrical shaft 15 b projecting from the center of the lower surfaceof the member 15 a. The plate-like member 15 a is contained in aterminal holding recess 16 b of the upper gasket 16.

The aluminum positive current collector 13 includes a base 13 a and apair of legs (connectors) 13 b and 13 b. The base 13 a includes a fixedportion 13 c, which is contained inside of the engagement recess 11 aand is fitted to the lower side of the positive lower gasket 18, and amount 13 d to be fitted to the lower surface 4 a of the cover 4 at aposition adjacent to the engagement recess 11 a. A through hole 13 epenetrating in a thickness direction is formed in the fixed portion 13c. The fixed portion 13 c and the mount 13 d which are stepwise disposedare connected via a vertical wall 13 f. The legs 12 b and 12 b areelectrically connected to and mechanically coupled to the electrodeassembly 3 via a clip 10 schematically shown only in FIG. 1.

The shaft 15 b of the positive external terminal 15 is inserted into thecylindrical portion 16 d of the upper gasket 16, the through hole 18 aformed in the positive lower gasket 18, and the through hole 13 e formedin the fixed portion 13 c in the positive current collector 13, andthen, the tip is widened under pressure, thereby forming alarge-diameter portion 15 c. Consequently, the positive externalterminal 15, the upper gasket 16, the positive lower gasket 18, and thebase 13 a of the positive current collector 13 are securely caulked andjoined to the cover 4. Moreover, owing to the caulking and joining, thepositive current collector 13 is electrically connected to the positiveexternal terminal 15.

The battery 1 in the present embodiment is particularly featured by thefollowing points.

First, referring to FIGS. 3 and 5 to 9, the rib 17 h is disposed at theouter peripheral edge of the flat portion 17 b in the negative lowergasket 17 interposed between the lower surface 4 a of the cover 4 andthe negative current collector 12. The height H of the rib 17 h (seeFIGS. 5 and 9) is more than the thickness of the base 12 a of thenegative current collector 12 c. The rib 17 h sufficiently ensures aninsulation distance defined between the negative current collector 12 cand the cover 4, thus securely insulating the negative current collector12 c from the cover 4.

In particular, at the flat portion 17 b of the negative lower gasket 17,the rib 17 h having the thickness more than that of the base 12 a(especially, the mount 12 d) is disposed at a portion corresponding to aposition at which the legs 12 b an 12 b project from the mount 12 d at aportion at which the electrode assembly 3 is electrically connected tothe negative current collector 12, and therefore, the negative lowergasket 17 can effectively insulate the negative current collector 12 cfrom the package (especially, the cover 4). At the base 12 a of thenegative current collector 12, the position, in particular, at which thelegs 12 b and 12 b project from the mount 12 d, need be securelyinsulated from the package (especially, the cover 4). Consequently, evenif the rib 17 h is not disposed over substantially the entire outerperipheral edge of the flat portion 17 b of the negative lower gasket17, unlike the present embodiment, but only at the portion correspondingto the position at which the legs 12 b and 12 b project from the mount12 d of the negative current collector 12 on the outer periphery of theflat portion 17 b, the negative lower gasket 17 can effectively insulatethe negative current collector 12 c from the cover 4. According to theconstruction above, a weight saving of the gasket along with theinsulating effect can be obtained.

Next, the expanded portion 17 a of the negative lower gasket 17interposed between the negative current collector 12 and the cover 4 iscontained in the engagement recess 11 a formed at the lower surface 4 aof the cover 4. Consequently, only the flat portion 17 b formed into athin plate in the negative lower gasket 17 projects from the lowersurface 4 a of the cover 4, thereby suppressing the projection of thenegative lower gasket 17 from the lower surface 4 a of the cover 4 tothe minimum. In contrast, the entire positive lower gasket 18 iscontained in the engagement recess 11 a formed at the lower surface 4 aof the cover 4. In this manner, the projection of each of the negativelower gasket 17 and the entire positive lower gasket 18 from the lowersurface 4 a of the cover 4 is suppressed to the minimum, andconsequently, the upper end of the electrode assembly 3 can be disposedsufficiently near the lower surface 4 a of the cover 4. Thus, it ispossible to increase the occupancy of the electrode assembly 3 withrespect to the volume of the battery cell 2, so as to enhance energydensity.

Moreover, the wall surface constituting the engagement recess 11 a atthe lower surface 4 a of the cover 4 is formed into a recess. Therecessed wall surface defines or restrains the position of the expandedportion 17 a of the negative lower gasket 17 contained in the engagementrecess 11 a. Specifically, the engagement recess 11 a formed at thecover 4 and the expanded portion 17 a of the negative lower gasket 17are brought into contact with each other not on the plane but in mutualengagement. As a consequence, the negative lower gasket 17 can beprevented from being rotated with respect to the cover 4. In the presentembodiment, the negative external terminal 14, the upper gasket 16, thecaulked portion 17 c of the negative lower gasket 17, and the base 2 aof the negative current collector 12 are caulked and joined with respectto the cover 4 via the rivet 22. The expanded portion 17 a of thenegative lower gasket 17 is contained in the engagement recess 11 a, sothat the rivet 22 can prevent the rotation of the negative lower gasket17 with respect to the caulked and joined portions. As described above,the rivet 22 is concerned in electrically connecting the negativecurrent collector 12 and the negative external terminal 14, andtherefore, the rotation of the negative lower gasket 17 at the caulkedand joined portions via the rivet 22 is undesirable in view of thesecureness of the favorable electric connection between the negativecurrent collector 12 and the negative external terminal 14. Theprevention of the rotation of the negative lower gasket 17 with thesimple configuration in which the expanded portion 17 a of the negativelower gasket 17 is contained in the engagement recess 11 a of the cover4 has a great advantage from the viewpoint of the favorable securenessof the electric connection between the negative current collector 12 andthe negative external terminal 14.

In addition, as shown in FIGS. 3, 6, and 7, the thickness T of thecaulked portion 17 c that is caulked and connected to the cover 4 in thenegative lower gasket 17 is set to be more than those of other portionsin the negative lower gasket 17. In this manner, only the thickness T ofthe caulked portion 17 c where a large force exerts by caulking is setto be large, so that the negative lower gasket 17 is reduced in weightand a material required for fabricating the negative lower gasket 17 isreduced while air tightness of the negative lower gasket 17 can beenhanced.

Additionally, referring to FIGS. 3 and 6, a clearance 31 is defined bythe wall surface (i.e., the engagement receiving portion 11) surroundingthe engagement recess 11 a at the lower surface 4 a of the cover 4 neara corner defined by the caulked portion 17 c and the vertical wall 17 din the negative lower gasket 17. In particular, a clearance having adimension indicated by reference numeral S1 is defined between side wallsurfaces surrounding the vertical wall 17 d of the negative lower gasket17 and the engagement recess 11 a. Moreover, a clearance having agreater dimension indicated by reference numeral S2 is defined betweenthe tip of the caulked portion 17 c of the negative lower gasket 17 andthe side wall surface surrounding the engagement recess 11 a at thelower surface 4 a of the cover 4. In this manner, the clearances 31, S1,and S2 are defined between both ends of the caulked portion 17 c of thenegative lower gasket 17 and the wall surface (i.e., the engagementrecess 11) surrounding the engagement recess 11 a, and therefore, roomcan be secured such that the caulked portion 17 is deformed (relieved)in a planar direction when the caulked portion 17 is compressed in athickness direction during caulking and joining. Consequently, it ispossible to securely prevent a damage such as a crack on the negativelower gasket 17 during caulking and joining.

The present invention is not limited to the embodiment, variousmodifications can be implemented. For example, although the presentinvention has been described by way of the configuration in which theexpanded portion 17 a of the negative lower gasket 17 is contained inthe engagement recess 11 a of the cover 4, a part of a gasket (i.e., acontained portion) may be contained in a recess formed at not the coverbut the inner surface of a battery case.

1. A battery comprising: a current collector including a base which isdisposed at an inner surface of a package and is electrically connectedto an external terminal and a connector which projects from the base andis electrically connected to an electrode assembly contained inside ofthe package; and a gasket including a body interposed between the baseof the current collector and the package and a rib which is disposed atleast at a portion corresponding to a position at the outer peripheraledge of the body where the connector projects from the base of thecurrent collector and has a height more than a thickness of the base ofthe current collector.
 2. The battery according to claim 1, wherein therib is disposed at a portion corresponding to a position at the outerperipheral edge of the body where the connector projects from the baseof the current collector.
 3. The battery according to claim 1, whereinthe body of the gasket has a flat portion of substantially rectangularplate shape, and the rib is disposed at the outer peripheral edge of theflat portion.
 4. The battery according to claim 1, wherein the gasketincludes a contained portion which is contained in a recess formed atthe inner surface of the package.
 5. The battery according to claim 4,wherein the base of the current collector comprising: a first portionwhich is disposed in the recess; and a second portion which is disposedat the inner surface of the package adjacent to the recess and in whichthe connector is provided; and wherein the rib has a height more than athickness of the second portion.
 6. The battery according to claim 4,the contained portion of the gasket includes a caulked portion which iscaulked and joined to the package together with the base, the thicknessof the caulked portion being greater than those of other portions of thegasket.
 7. The battery according to claim 4, wherein a clearance isdefined between the surroundings of the contained portion of the gasketand the wall surface of the recess of the package.